This invention relates to the field of two way voice and data communication, and more particularly, to the control of transmission between a multiplicity of portable radio/data terminal units and a large host computer.
There are known applications using large computers with interfacing units to control many data input terminals. One such is used on a large factory assembly line where products on the line may require special components, and data regarding the individual orders is stored in a host computer. As the product units move down the line, an operator can go to a data terminal, usually of the CRT display type, and query the computer as to the requirements for a particular product unit. The computer will, of course, come back with the appropriate information almost immediately, but the operator must then return to the unit which is moving down the line and carry out the instructions given him. Another disadvantage of this system is that each data terminal is polled in a fixed sequence for data to be sent to the host computer. After each unit is polled, the control unit waits a few seconds for a response. Since one control unit can be connected to as many as 32 data terminals, there can be a perceptible delay in the receipt of the desired response back from the host computer. An added disadvantage is that each data terminal requires a television type coaxial cable.
While such a system is usable in a factory, even with the obvious handicaps, it becomes completely impractical for an application such as a ship yard or train yard where mobility as well as instant two-way communication with the host computer is essential, and communication between data terminals is desirable.
In another application involving the use of multiple paging units and a transmitter, each pager is assigned a unique two-word binary coded address. In U.S. Pat. Nos. 3,801,956 and 3,855,576 assigned to the same assignee as is the present invention, a system is shown for detecting the pager address asynchronously and for detecting the combinations of the address words and their complements. There is no two-way communication, the pager user merely being alerted to one or more actions to be taken.